As cloud computing develops, speed and frequency of an optical communication network are made higher, so that it is demanded improvement of optical modulation efficiency. As to an optical modulating device, for realizing matching of speeds of micro and light waves, it has been known to make a thickness of an optical waveguide substrate, composed of a non-linear optical material such as lithium niobate, very small and to adhere it to a separate supporting body. In this case, it is proposed that a conductive film is formed on the supporting body and the supporting body is adhered to the optical waveguide substrate through the conductive film, so as to prevent ripples in transmittance characteristics of micro wave due to the resonance of the supporting body (Patent Document 1; Japanese Patent Publication No. 2003-156723A). Such conductive film includes gold, silver and copper of a low resistance.
Generally, for lowering the wiring resistance, it has been used a gold (Au) electrode having a high electrical conductivity in many cases. In the case that an electrode is composed of a chrome film or the like, it is difficult to lower the resistance of the electrode to a necessary value so that designing of the electrode is difficult for attaining the necessary resistance value.
Further, according to a travelling wave-type optical modulator described in Patent Document 2 (Japanese Patent Publication No. 2002-040381A), it is proposed that an underlying film made of chrome film is formed on a lithium niobate body and gold plating is provided thereon to provide modulating electrodes modulating light propagating in an optical waveguide.